Logo
Please visit our Sponsors

FAQs about Specific Gravity, Salinity 2

Related Articles: Specific Gravity, Salinity, Product Review Marineland Labs/Aquarium Systems Hydrometer, Part 1 By Steven Pro, Choosing Synthetic/Natural Seawater, Major/Minor Seawater Constituents, Frequent Partial Water Changes

Related FAQs: Spg 1, Treating Tapwater For Marine Aquarium Use, Seawater, Seawater 2, Seawater 3, Seawater 4, Seawater 5, Seawater 6, Reverse Osmosis Filtration, Test GearUsing Hyposalinity to Treat Parasitic Disease,

Some animals are more touchy to changes in spg than others. Phil Sokol's fab pic of a Robust Hairy Ghost Pipefish.

Refractometer Regulation       10/5/15
Hello and much admiration of your knowledge and expertise. I hope you might have the answer to a question about my RedSea refractometer. I have used it since onset of my newer (six months) aquarium but as of recent it reads very high. The directions specify to clean using reverse osmosis water and I do so consistently.
<Have you tried rinsing it; as in overnight, in freshwater? >
It seems though whenever I measure my aquarium water the refractometer reads at or above 1.030. However my lfs read the same aquarium water on the same day as 1.025. The tricky part is that if I rinse the refractometer under hot tap water it adjusts back to 1.025.
<Ah yes; salts crystallization in the unit>
My question is whether it is acceptable to rinse (not submerge) the unit?
<Yes; should not cause trouble>
Is this a normal process of getting stuck like a plastic hydrometer?
<Mmm; yes>
The refractometer advertises that it is calibrated for reef aquarium temperature, not that I accurately understand, but I'm trying. I don't want to make any rash changes though, all inhabitants appear satisfied and water tests seem to confirm. The issue of basic salinity is of obvious concern, does this sound like something the manufacturer could assist with?
<Oh yes>
It came with a tool for calibration but also claims to come already adjusted.
<It is>
Do refractometers typically require fine tuning and what indicators for this might appear?
<Good ones do NOT require calibration, nor adjustment>
Your assistance is invaluable. One other silly thing, when measuring salinity or getting a sample for water test tubes is it pertinent to take the water from a certain depth or area (65 gallons if relevant)?
<In modern set ups it is not; as they are circulated such that thermal et al. stratification is discounted>
Or is it accepted to just take the upper layer of water to avoid inserting my hands unnecessarily?
<The surface should be fine. Bob Fenner>

Re: Specification of pH from Nestle Water; now SG     2/4/15
Hi Bob,
<Adam>
A mate of mine and I had a falling out and he was the only guy that also kept marine fish that had an RO.
After the conversation below bnw it is the dry season I need to top up and ran out of rainwater.
Where I am we use well water (not that primitive we have electric pumps) but anyway I think even an RO would struggle.
<Can't tell from here... need analysis, or just trying... there are modules, modular units that can handle most anything... taking out particulates and more ahead of the tris membrane>

Therefore before I try and source other human packaged drinking water what SG are fish generally able to go up to?
<... ?... depends on what species, and to extents, what they've been exposed to>

What are the symptoms of too high SG, all are ok now but a Blueface has blotches maybe due to SG stress but is still swimming and eating normally.
<... See WWM re the subgenus Euxiphipops... not easily kept. To answer your question directly; I would not continuously keep full-marine organisms in higher than 1.025-6 at temp., Red Sea ten percent higher>
Kind regards,
Adam.
<Keep reading. Bob Fenner>
Re: Specification of pH from Nestle Water; spg f'        2/5/15
Hi Bob,
<Adam>
All the other fish are ok so I do not think it is a disease,
<Me neither; i.e. not pathogenic, but environmental>
here are the parameters in a clear format from Nestle the manufacturers.
I am in a remote place and to get an RO will take several days at best even if in stock about 750kms away.
Anyway I think from your earlier comments the Nestle Pure Life will be the best option.
Any copper will be removed by the Polyfilter.
I must do something quickly.
What do you think, pH seems wide but I have Seachem's Reef buffer which works very well if it drops.
<Only adjust through water changes; and then slowly>
Right now it is spot on at 8.3 Nestle Pure is all go?
<Okay>
Minere
pH - 6.5 - 8.5 (seems very wide)
<Is... by two orders of magnitude! How do/did you get these measures? Provided by the manufacturer, Nestle.?
>
Total hardness 100 - 110mg/l
Nitrate less than 0.4mg/l
Nitrite less than 0.007mg/l
Ammonium less than 0.013mg/l
Manganese less then 0.2mg/l
Calcium 20-30mg/l
Magnesium 7 - 9mg/l
Sulphate 60 - 70mg/l
Bicarbonate 200 - 300mg/l
Chloride 100 - 130mg/l
Nestle Pure Life.
pH - 6.5 - 8.5 (seems very wide)
Total hardness 80 -90mg/l
Nitrate less than 0.4mg/l
Nitrite less than 0.007mg/l
Ammonium less than 0.013mg/l
Manganese less then 0.01mg/l
Calcium 20-30mg/l
Magnesium 7 - 9mg/l
Sulphate less than 5mg/l
Bicarbonate 200 - 300mg/l
Chloride 2 - 4mg/l
<If this is all you have... I would use it. Bob Fenner>
Re: Specification of pH from Nestle Water       2/5/15

Hi Bob,
<Adam>
I thought it better to do something as you are in a far away place, lol, every day it is hot here and the SG was already 1.029
<I'd be diluting this per the SOP on WWM... about a thousandth per day>
and the Blueface was looking bad. Strangely I think I am more worried than he is as he is still eating and grumpy with the Regal Tang who he tries once or twice as day to catch but the Regal is so much faster, the rest of the time they ignore each other. So I purchased some Nestle Pure Life and added enough to hopefully take it down to 1.027. I do not want to take it down too fast not only for the fish but nitrogen cycle bacteria etc
<You are wise here>
I will wait 24 hours and add some more and take it down eventually to normal. I will update you and your readers.
Kind regards,
Adam.
<And you, BobF>

Hyposalinity in The Display Tank.. An Acceptable Tradeoff?  12/28/07 Hello fellow fish addicts, <Scott F. in today!> First the specs: 3 year old 75 gallon marine FOWLR - 90 lbs live rock, 75 lbs live sand HOB filter with 2 bags of Tempura and some powerheads totaling about 14X/hr turnover Corallife SuperSkimmer 125 80 watt fluorescent light 500 watts worth of submersible heaters temp - 79F, ammonia 0, nitrite 0, nitrate about 20ppm, pH 8.0 Livestock (length") Klunzinger wrasse 8" Yellow tang 4" Huma Huma trigger 5" Flame angel 3.5" Emperor Angel 6" Domino Damsel 2.5" *female blue-throat trigger 2.5" (see below) <Wow...a bit of a crowd for the long term, really. Do consider larger quarters for the near future!> The situation: I received some rock to set up my new 180 (to which all inhabitants of the 75 were going to be transferred to) and got a hitchhiker - a female blue throat trigger in a puddle at the bottom of the LR container. Idiot that I am, I tossed the little gal into the 75. A week later everyone has a mild (at least to the eye) case of Crypto. Due to the size of the fish, as well as, room and financial constraints - I am unable to remove all of the fish from the display tank and provide them with adequate sized hospital tanks for medicinal treatment. Of note - the Emperor Angel looks like he has some secondary infections/disease (film on one eye, splotchy color). <Often occurs with Ich and other parasitic illnesses. The fishes are usually weakened by the initial infection.> My question: Since the tank is a FOWLR without macros or inverts would it be workable to hypo the whole display tank? My main concern is whether or not the beneficial bacteria in the sand and rock will survive. I plan on keeping the SG at 1.009, will do regular water changes (every 3 days or so) during the treatment, Amquel and refractometer are on hand and fresh Tempura is waiting to go. I'm aware that there will be "die off" of worms, pods, coralline, etc, but am hoping that water quality can be maintained via the above measures/tools. What do ya think? Thank you for your time and consideration, Eric <Well, Eric, if you do understand that there will be some collateral damage as a result of the hyposalinity, and if this is acceptable to you, then go for it. I am almost always against treatments in the display aquarium for this very reason, but I would rather see you use hyposalinity than some harsh medicines in the display aquarium. Best of luck to you. Regards, Scott F.>

Deep Sand Bed, Low Salinity System 9/21/07 Hi. Greetings from Alaska. <Hello from Chicago.> I have a 55gal. FOWLR with quite a bit of fish. Bicolor angel, Raccoon B/F, Fox Lo, Royal Gramma, Flame Hawkfish, Tomato clown and a Yellowtail damsel. <I would call that very heavily stocked, even overstocked.> I am a big fan of hyposalinity system and that is not as a treatment but as a method of my hobby. <I have to disagree with you here, keeping fish in anything other that natural as possible conditions is exceedingly stressful over time and leads to an early demise.> I am running this tank for more than a year now and I have no disease or any problem on my fish during this period. <Unfortunately I don't think this will last over the long haul as the conditions take their toll.> I am planning to buy a HOB refugium and make a deep sand bed in it. My question is: Can a anaerobic nitrifying bacteria form or thrive in a deep sand bed with a salinity of 1.010 SG? Thanks for your response. Larry <The bacteria will colonize this area, there are many species that live in all different salinity levels. However I encourage you to reconsider your approach.> <Chris>

Refractometer vs. Hydrometer question    11/27/06 Dear Crew, <Dear Eric, Mich here, hello to you on the first day of deer season.> I have been using a Red Sea Hydrometer for as long as I've been in the hobby which is about a year now. I decided to upgrade to a $60 Hand Held Refractometer w/ATC on sale for $30. <Good investment.>  I calibrated it this morning by setting the room temperature to approx. 68 degrees F. and a couple of drops of distilled water as directed. I then proceeded to test some buckets of pre-made salt water. To my astonishment every bucket was 1.028 SG. I went to my main tank and it was 1.0275, which is probably due to it being 78 degrees. My quarantine tank was the same. My hydrometer has always read 1.0235 consistently. I would do this 3 - 4 times in a row to ensure the result was consistent if not accurate. <As you know consistency and accuracy are two different measurements, both equally important.>  I thought it might be off by .001 but not .0035 - .004.  <Hydrometers are notoriously inaccurate.> Thankfully all the corals in the tank are doing fine. <Good.>  I only have two fish: a blue/green Chromis and a Hippo tang who thinks he's a Chromis. The tang has some scarred looking flesh which has been there since a week after I got him. Could this be from too high SG? <Could be may things.>  (it's a grayish color in patches and his tail has looked frayed forever. The cleaner shrimp enjoys picking at him when the fish lets him.) <Good.>  Is it possible that the Refractometer is also off? <Doubtful.>  Should I trust the refractometer <Yes.> and slowly drop back to about 1.025 or 1.024 over the next few weeks during water changes<Yes.>? I think I'll bring a sample of water to the LFS to double check before I do much of anything, <Good...if they use a refractometer.>  but I would like to hear what you have to say. <I would trust the refractometer, not the hydrometer.>  Is it normal for Hydrometers to read low? I've heard they can read high, but not low.  <Hydrometers can be inaccurate in any direction.> Thanks for your time - Eric <Welcome.>

Measuring Salt Content - 10/25/06 Hi Eric, <<Hey Ken>> I finished the tank, filled it up, turned it on, and no leaks. <<Yea!>> What a relief. <<Indeed>> I want to test the SG in the tank.  I have a Blue Line ( I think) model RHS-10ATC refractometer.  I get a reading of 1.025 on this.  I also tried a Coralife "Deep Six" hydrometer and get between 1.021 and 1.022.  Does this seem normal to have this kind of range? <<Sure...the plastic box-type hydrometers aren't consider very accurate, but they are generally close/consistent enough for hobby use and are convenient for "quick" checks, especially if you have something like a properly calibrated refractometer to use for reference.  Personally, I prefer to use an electronic meter for measuring salinity but what you have should be fine>> Thanks, Ken <<Always welcome.  EricR>>

Meniscus...Is It Up Or Down? - 10/12/06 Dear Crew, <<Hello Eric>> Thanks for all the help you have given me in the past. <<Quite welcome>> I currently use a floating hydrometer/thermometer to measure the specific gravity in my tank and replacement water. <<Mmm, not very accurate...unless you have spent money for one of the better "lab grade" hydrometers (they generally don't contain "thermometers") as offered by Salifert, and pay attention to/have a conversion to allow for water temperature>> When using such an instrument, I have noticed that there is a reverse meniscus (shaped like a ' n ' instead of a ' u ') around it.  Do I read the specific gravity by checking the level of the water surface or where the reverse meniscus reaches?  I know usually a meniscus is read from its base but I have never dealt with a reverse meniscus, if that's what it is called. <<Hmm, describing the meniscus as either an 'n' or a 'u' is a matter of interpretation I think.  Regardless, read the hydrometer where the surface of the water just outside the meniscus would strike it>> Thanks, Eric <<Regards, EricR>>

And then there were none... substantial obeisance, hydrometer accuracy, troubleshooting SW illness...  - 09/14/06 Hi, You guys were a tremendous help to me last time, I went to Amazon and ordered anything with the name Fenner on it. (great books) A little background on the tank. I have a 50 gallon saltwater tank, 2 years old. pH normal, Nitrates normal, Nitrites normal, SG 1.022, temp.77-79, Nh3 negative. 30 Lbs live rock, and a 1.5 inch bed of live sand (infested with what I think are bristle worms, little orange things that are grey at the end). The lights run 10 hours a day, and I have a very healthy growth of bubble algae and the like. ( the tang loved it ) In the last three weeks I have lost,,,,  A yellow tang, 2 clowns, 5 assorted damsels, a mandarin (sob!) <Yikes>   and a citron goby. I have introduced an anemone, and a feather about two weeks ago, but they seem fine. <... likely the Anemone is involved, related to your fish losses here> My crabs and snails are all fine, but I tried to put in cleaner shrimp to help stem the massacre, and they died about 20 minutes after being put into the tank. (do I need to recalibrate my hydrometer?) <Doubtful... but I would "check" it against a known-to-be more accurate device... and raise your spg to 1.025> The fish were coated with a grayish mucus especially noticeable on the eyes, I have cultured the water <Neat!> and found Gram negative bacteria such as, Proteus, and Pseudomonas. <Very common "similar" microbial involvement in all marine waters> The fungal culture will take a bit longer to grow. I rarely do water changes, but the tank evaporates about 2-3 gallons a week that I refill with RO water. I have a canister filter that the LFS guy says not to touch "if your water is so clear, and the parameters are so good, don't even clean it, you will kill the bacteria that  live there", so I added another smaller canister filter. <Mmm... am not a big fan of this technology for the vast majority of marine systems. See WWM re> I don't know what to do, this has happened at the end of last summer as well, and I simply left the tank empty for 6 weeks to crash any parasites that were there, and then added fish and they were fine, but this time I don't think it was parasites. HELP PLEASE!! many thanks, josh <Well... Please read here: http://www.wetwebmedia.com/anemcompfaqs.htm and here: http://www.wetwebmedia.com/marine/setup/filtration/marineFiltr.htm and the linked files above.... And consider adding a protein skimmer if you don't have one, better filtration period, trading in the Anemone... Bob Fenner>

Supplying the refractometer  - 09/14/06 Dear Sir/Madam, we are manufacture and export all kinds of optical instrument, such as refractometer, microscope, photoelectric colorimeter, telescope, gem tools, etc. . Please go to see our URL, www.newera-optical.com. Should you require further information on our products or services, please send email us. We will make prompt reply. <Will post your URL, offering. Bob Fenner> Best wishes, Norna WU Hunan New Era Industrial Trade Imp. And Exp.Co., Ltd. 417 Bayi Road, Changsha, Hunan, China Tel: 86-731-2252760 Fax: 86-731-2250570 E-mail: james_dai@hneco.com URL: www.newera-optical.com msn:nornaruyi_wu@hotmail.com

Salinity and temperature relationship?   8/31/06 Hello to who ever maybe answering today and thank you in advance. <And good morning to you.> My question is about trying to understand the relationship between temperature and salinity in a marine aquarium. During the summer months my tanks tend to hover around 82 - 86 degrees, at this temperature I try to keep the salinity at 1.017 in my quarantine tank and 1.019 in my main tank - am I correctly understanding the relationship between the ambient temperature and its affect on salinity levels? Or should I try and maintain my tanks at higher salinity levels regardless of the ambient temperature? <Personally, I like 1.023-1.024.  At this salinity, more beneficial elements are in the water, as more salt is needed than would be at 1.019.> I recently was in Singapore where I visited a marine fish farm - they were maintaining salinity levels of around 1.023 - 1.026 depending on the species (higher salinity for Red sea varieties) and their ambient temperatures were around the same as what I am experiencing. <As far as the temperature/salinity effect, the change in salinity versus temperature has little or no effect in the average ambient temperature range we live in.> As always your advice would be very helpful. Kind regards, <You're welcome.  James (Salty Dog)> Aehsun

Refractometer/Calibration Question   7/24/06 Hi, <Hello Joe> I recently purchased a handheld refractometer.  I know most of your crew has stated the glass hydrometers are the most accurate, but from everything I've read, the refractometer should be close enough. <In my opinion, the refractometer is more accurate.> <<Is much more accurate AND precise. RMF>> Here is my question though.  The calibration instructions say that I should use distilled water and get a reading of 0.000 when the temperature is 20 degrees Celsius. <Joe, I believe they are referring to the water sample being 68 degrees.  Just refrigerate the distilled water to a temperature of 68.> (As you know, 68 degrees Fahrenheit).  The refractometer has ATC.  My house is always at 76-77 degrees.  I live in Florida (July at this time) and getting my house down to 68 degrees for a calibration event would put quite a load on my central air conditioner.  Am I okay to calibrate the refractometer at 76-77 as long as I continue to use it in the same temperature?  Are there any mathematical adjustments I need to make? <If the temperature if off a couple of degrees, it isn't going to affect your reading enough to matter.> Also - from everything I've read, it seems I should shoot for a SG of 1.025 <I'd shoot for 1.023.> as I am starting up a reef tank (150gal - currently cycling with LR and sand + algae refugium).  The temperature in my tank is If I have asked anything I should have found on your site already, I do apologize, but I swear I have been looking for the answers to these questions for about a week now! Thanks very much for your time.  Keep up the great work. <You're welcome, James (Salty Dog)> Joe in Tampa
Re:  Refractometer Calibration Question   7/24/06
Hi again - thanks for the quick reply.   <You're welcome.> However, I'm still not completely confident my refractometer is that easy to calibrate.  This is from the instructions -hopefully I'm missing something. Make sure the ambient room temperature is correct for the solution you are using (20degreesC/68degreesF). <Yes, confusing here..."Make sure the ambient room temperature is correct...."  It reads like, different temperatures for different solutions??> When working temperature of the room or environment (not the sample) changes by more than 5degreesF, we recommend recalibrating to maintain accuracy. If the instrument is equipped with Automatic Temperature Compensation system, the ambient working temperature of the room must be 20degreesC (68degreesF) whenever the instrument is recalibrated. Once calibrated, shifts in ambient temperature within the acceptable range (10degreesC-30degreesC) should not effect accuracy.  So - since this one is equipped with ATC, what do you think? <I guess I'd calibrate it to the temperature they state.  And, as they state, temperature fluctuations of 10 degrees should not affect accuracy, which is what I mentioned to you in the previous email.  Calibrate it to the temperature they suggest, and feel comfortable with your readings thereafter.> Thanks again. <You're welcome.  James (Salty Dog)>

Conductivity to Specific-Gravity Conversion Formula? - 05/11/06 Hi, <<Hello!>> I was wondering if you guys know the formula for converting conductivity to specific gravity (salt water)/salinity. <<Off hand no, have never seen conversion tables for this particular conversion either.  Maybe try asking the question to Randy Holmes-Farley on the RC chemistry forum>> In particular, I would like to convert the conductivity reading from my Neptune Systems Aqua Controller 3 Pro to a SG reading in the range of 1.020-1.025 (sample values). Formula: SG = Conductivity * (factor) @ a given temperature (78F). <<Short of finding a conversion table for 'conductivity to specific gravity', you can convert conductivity to 'salinity' using the table starting on page 10 of this manual ( http://72.14.207.104/search?q=cache:9Onbm2457AkJ:www.lamotte.com/pages/common/pdf/instruct/cds5000.pdf+ CONDUCTIVITY+TO+SALINITY+CONVERSION&hl=en&gl=us&ct=clnk&cd=8)...and then convert salinity to 'specific gravity' using the table in this manual ( http://www.piscespub.com/sgpub.pdf)>> Thanks for the help. Vic <<Regards, EricR>>

Hydrometer Readings  3/16/06 Hello there, <Hi Czarina - Tim answering your question today!> We have just set up a new 40 gallon aquarium. It currently contains nothing more than saltwater and live sand (with sump, bioballs, heater set to 77, pump etc). However, EVERY time we test the water with a hydrometer we get a completely different reading. Sometimes the needle hits the very top of the meter, then 3 seconds later the bottom, then somewhere in the middle (not necessarily in any particular order). We went and bought a second hydrometer to double check, and exactly the same thing is happening. We are taking these readings without leaving any time between them- so there is no room for any fluctuation. We have not added salt for a few days either. The guy in our LFS said there is no way this could happen. Also, it seems that when we put it under and hold it there, we get a higher reading it seems- than if we fill it and lift it out quickly. <It could be that you have bubbles stuck to the needle when you first fill it, causing it to jump high, then fall once the bubbles come off. Alternatively the needle could be getting slightly wedged at the bottom. In any case, fill the hydrometer to the recommended level - and ensure that your water is at the appropriate temperature for measurement (should be ca. 25C for most hydrometers but check the instructions supplied by the manufacturer). Then, depending on the model and whether or not possible, place the hydrometer on a level surface - e.g. a table top or similar. Tap the outside of the hydrometer (if it is plastic - not glass) with the tip of a pencil or pen a couple of times to dispel any bubbles in the hydrometer. Then allow the needle to stabilize and you should have an accurate measurement. I think the answer really is down to physics here!> I am completely and utterly confused as to why this is happening. This crazy fluctuations can't be possible <Exactly - they can't unless something on the needle is causing this such as an air bubble.>. Please advise us! Thank you for your time, <Always a pleasure!> Czarina.

Dilution Equations    3/2/06 Hello <Hi Fargo. John here this afternoon.> Spent several hours on the web and your website.  Couldn't find much to help, but I was wondering if you guys might have an equation that would help estimate how much fresh water needs to be added to lower the specific gravity of an aquarium by a certain amount.  I have tried the standard equation of m1v1=m2v2 but have not been able to make it work. <Conservation of momentum? uh?> Then after I lower it, need to figure out how to increase very slowly as to not stress the fish.  Trying not to take a shot in the dark and do it as controlled as possible. <regardless of what you do, I wouldn't increase or decrease the specific gravity by more than around 0.002 at any one time. For determining the quantity of freshwater, it really is easy my friend - just need to calculate a ratio: Resultant specific gravity = (Vol1.SG1 + Vol2.SG2)/T Here, Vol1 is the amount of water remaining in the tank, and Vol2 is the amount of water you are changing T = tank capacity (Vol1 + Vol2 = T). SG1 = specific gravity of water in the tank SG2 = specific gravity of change water.> Cheers and Thanks <Welcome! John.> Fargo

Pinpoint Salinity Monitor Problems 2/18/06 Hi gang,  I've run a Pinpoint ph monitor on my reef system for several years. . . overall I'm pleased with it, although it has to be run with a 9 volt battery. . . two attempts at using the optional adapters provided by the manufacturer went astray -- I had a techno-geek friend test the second one after it shorted out my unit for a while. . . turns out the adapter was supplying 11.8 volts. . . way too high, and almost destroyed the monitor. The salesperson at my usual internet supply source confirmed the adapter unit is cheap/unreliable. <Indeed, the power supply problem is well known among Pinpoint users, and you would think they would supply a better quality unit, but alas... pinpoint monitors are made to be inexpensive hobbyist models.  Top of the line models cost much more.> On to my real point. . . a month ago, I ordered a Pinpoint salinity monitor. After calibrating the unit, I added it to my reef tank. Readings were WAY high and fluctuated wildly. I called the supplier. . . who was immediately aware of the 'problem'. Turns out the unit won't function properly in proximity to electrical current. . . e.g. my power compact reef lights. Since the only places available for mounting on my system are a crowded sump with several hundred watts of pumps being powered up (returns and downdraft skimmer pumps) and the top of my reef tank, there's nowhere I can run the relatively short (less than three foot) probe-and-cord to use the unit. I feel like I've effectively purchased a hundred-dollar-plus paperweight. As the last straw, the unit ate up a 9 volt alkaline battery in just a week's worth of use. The thing is, there's no disclaimer describing this problem on the website where I bought the thing. And the supply source wasn't willing to allow me to send back the unit to upgrade for another Pinpoint product. So 'caveat emptor' on this one. . . Chuck <It is a shame that this problem exists, and pinpoint should probably at least state in the instructions that the unit must be away from such interference, but again, these are entry level inexpensive products.  Your comments are appreciated and will be posted amount the FAQ's.  Best Regards.  AdamC.>

Refractometer Accuracy  1/20/06 Hi WWM, from snowy Nevada!! Hope there is better weather where you are! <Ah yes. A beautiful day in Georgia.> I have a refractometer that is approx. five years old. I recently had reason to question the accuracy of the meter, when someone else was testing the same sample water with another refractometer and received a completely different result than my refractometer.  Both refractometers had been calibrated. I purchased another refractometer as did someone else I know. We took all 3 refractometers and calibrated them at the same time with the same water. Then took some sample aquarium water and tested it with all three. My five year old refractometer tested the water at 1.025, my new refractometer tested it at 1.025, and the third refractometer tested it at 1.022.  Is this a significant difference between meters that should be of concern? <Not really.> It seems the results should have been more similar, given that all three were calibrated in the same way, at the same time, with the same water. <Actually, most are only accurate within the certain temp. planned for their use. Probably what is the case here.> Another notable tid-bit, both of my refractometers have the same model number RHS-10ATC, and the third has a model number of ZGRS-10ATC. Could this just be the difference in models? <Yep. Probably meant for best results in certain temps.> None of the meters list any kind of accuracy reference. Which should we consider more accurate? <Try to find out the intended temp. for each. As long as you get consistent results from the one you are using, you should be fine.> I am very curious to hear your thoughts. <Oh, and I do have some curious ones!> Thank you very much and have a great night (hopefully in some tropical location)!! Jen Marshall <Hmm...Tropical? Well, there are some "strange birds" around here! - Josh> Rising salinity   1/17/06 Hi,<Hello Ben> I have a question about my 75 gallon reef tank.  The salinity keeps rising a lot.  I know that it will rise because of evaporation but the salinity in my tank is rising I think much faster than it should.  Last night I did a water change and it was 1.028 (which is high but I was planning on gradually bringing it down), when I measured it this afternoon it was at 1.030 and barely any water in the tank was gone.   Do you have any idea what could be causing this and what should I do? <It's impossible for the salinity to rise without adding any salt.  I'm guessing the problem lies in your testing device or how you are using it.  If you are using an Instant Ocean or Coralife you need to be sure no bubbles are sticking to the indicator arm.  This will give you a false high reading.> Thanks a lot, <You're welcome.  James (Salty Dog)> Ben
Re: Rising salinity   1/22/06
Thanks for the response. <You're welcome> I bought a refractometer but my salinity is still really high.  could my protein skimmer or something be taking out a lot of water and not salt? <No, we would all have that problem then.> I don't know if that's possible but that's all I can think of.  If you have any ideas that would be great. <Now that you have a refractometer, slowly remove saltwater and replace with fresh at a rate of .001 per day till you achieve the level you want. When mixing saltwater for water changes do not test salinity until the temperature level reaches the level of your display tank. Lets go from there.  James (Salty Dog)>

Salinity problem 10/31/05 I am starting a 55 gallon saltwater tank up. I have not cured the tank yet. My problem is the salinity. One side of the tank reads too high and the other side reads too low. I have four powerheads running at all times. The temp is perfect, the pH is fine. How do I fix the salinity? Oh and I am using a swing arm hydrometer to measure. <Sounds like you have inadequate water movement. Powerheads are a horrible way to move water in an aquarium, though they are cheap. Please see http://www.advancedaquarist.com/issues/sept2003/short.htm for some great water movement info> Any recommendations will do.. <Hope I've been a bit helpful> New to saltwater tanks <Definitely read everything applicable on this site, and check out the Advanced Aquarist archives as well. Good luck, and feel free to email us with further questions! M. Maddox> 

Water Change Mistake, Specific Gravity Level 10/7/05 Hi guys, <Hello Mark.> Thanks for all you do through the WWM site. It's been invaluable to me as I work with my tank.  <Glad to her we have helped.>  I have a 58 gal Oceanic Reef Ready with about an 8 gallon wet/dry. Tonight I was doing my weekly 10% water change and inadvertently refilled with RO/DI fresh water from the LFS. Imagine my chagrin when I realized it! <Uh-oh.> My sg is now 1.021. I think it was around 1.023 before the change. I haven't run a panel on the water to check Ph, Alk, yet. The water had been buffered, so at least there was that. The question: Will my two clown fish, 20 hermits, 20 turbo snails, or live rock be adversely affected by the rapid drop in sg? <As you already know this SG is a bit low. Having said that while it is not an optimal level if you slowly bring it back to normal through extra water changes over the next few days I would not expect to see any long term damage. Should you see any die off I would expect it to be your invertebrate life not the fish.> Kicking myself for not "taste testing", <A refractometer is your friend.> Mark <Adam J.> 

Salinity  09/13/2005 Hi Crew,   I live in Jamaica where our temperatures average in the 90's. I have a 200 gallon marine tank FOWLR, the water temperature is in the high 80's and I was wondering what salinity I should keep my water at?  <Temperature and salinity are really non related as far as any significant change that would occur.  But, to answer your question, anywhere between 1.021 to 1.025.  James (Salty Dog)> <<Mmm, but the hydrometers most folks use are calibrated for lower temperatures... I would keep the apparent density near 1.021, 1.022. RMF>>

Salinity Hello guys! <Hello, Jamie> BTW love the site! I always find exactly what I need here. Last week I had to move my 200gal saltwater aquarium to the other side of the house because of new floors going in (Remind me not to do that again!!) Of course, I had to remove all the live rock, chase down my fish, and drain the entire thing. I practically did a 100% water change. Now my salt level is low.....like, 1.017 according to the Deep Six thingy, but all the creatures are doing fine. I guess I just didn't add enough salt. I will be moving the "bad boy" back tomorrow and in the process try to raise my salt levels back to 1.026. I plan to just drain and restore the water. Can I just add more salt to the existing water then put it back in? My fish are pretty tolerant of a little change, but I am worried about the stress of two moves and raising the SG all at once. Please advise on what you would do.  <Jamie, with a tank as large as yours, I would take out three gallons and add salt to that to mix to a 1.030 level and return to the tank once the water is cleared up.  I'd do it daily until you reach your desired level.  James (Salty Dog)> Jamie

- New Red Sea Continuous Use Hydrometer - Have any experience with these or heard anything about them. <They are a recent appearance on the market and we don't do product testing per se... so I've not actually used this item yet.> We are considering bringing them in, but of course if they will cause our customers more harm than good, we don't want to.  Are they accurate enough for general salinity monitoring in fish systems? <Swing arm hydrometers are generally accurate within their own calibration for a year or so, after they crust up they test to become less accurate. If they are off by a couple of ten-thousandths, then they will be consistently off by that amount over their range. The only way to known the accuracy of a swing arm hydrometer would be to test it against a refractometer.> We don't have a sample to test against a refracto at the moment so I was hoping you knew. <No clue really... even with a batch of 100, you're going to find some variation.> Matt <Cheers, J -- >

Salinity in 350 gallon tank Hi,  <Hello James, nice name> Just a quickie about salinity. I have fish from Kenya (2), far east (7) and a couple from the Red Sea. My LFS guy says to keep my water at 1.022 I have done this for over a year. Is this ok, especially for my Red Sea fish? Everyone is looking good anyway.. <James, everyone has their own preference for salinity. Personally I keep my tank at 1.024. Red Sea fish seem to do a little better at that salinity. If things look good, why change. James (Salty Dog)> Many Thanks, James <You're welcome>

Problems after salinity increase 3/6/05 I recently raised my salt level (it was pretty low). In the last two days I noticed one of my emerald crabs dead, my xenia has shrunk and my brittle star has lost an arm and had some white spots on him. Should I wait, do a water change or other? Thanks, John  <Salinity changes are very hard on inverts, and what you are describing is probably due to this change. I would suggest increases of no more than 0.003 (1.017-1.020 for example) in any one day and giving the animals a couple of days to acclimate. If you have been more aggressive than this, I would just give everything a few days to acclimate (trying to drop the salinity back down will just add to the stress). Also, I would strongly suggest checking your salinity measuring device against another aquarists, a local fish store or a refractometer. "Swing arm" style devices are notoriously inaccurate. Best Regards. AdamC.>

Specific Gravity I just went to get my water tested at my LFS and I have some questions. I took a plastic baggie and took water from the surface which I shouldn't have done. They used a refractometer and they said the sg was 1.028 and I told them I used a Coralife hydrometer and it was 1.024. They told me the Coralife is usually 4-5 thousands off so I should bring it down to 1.020 on the Coralife hydrometer which will be 1.024 on the refractometer. Do you think this is true?  <Joe, I would trust the refractometer, they are more accurate. James (Salty Dog)>

High Salinity 28 Jan 2005 I have a problem..... the salinity in my tank is too high. Is the only way to solve this to change some of the water. <You have to have a way to dilute the salinity so the short answer is yes.> There are no fish yet or anything else. <Good luck, MacL>

Hydrometer Accuracy (11/21/04) Steve, <Greetings again. I've been out for a while.> Thank you very much for the responses. <My pleasure.> I appreciate it. For the salinity and temperature, my tank temperature right now is between 77.1 and 78.1 - depending on whether the MH lights are on or not :-)  Thanks for that info. Also, you asked about the price of my refractometer, here is the link for it - http://diyreef.com/shop/index.php?cPath=21&osCsid=4c612be0269caed832730465e3 6f8358.  If you click on "refractometer" in the column on the left side under Products, you will see it.  The price is $43.00. Thanks again, Paul <I would not trust the "temperature adjustment" of the salinity scale of this inexpensive hydrometer. It is using a fixed scale, so the salinity can only be trusted within the stated narrow range of temperatures. As mentioned, I'd stick with specific gravity as most folks use this, so it i.e. easier to communicate. Use a published graph to convert to salinity at specific temps if you want to know this value. Steve Allen.>

Re: Eel oxidized, help! Epsom, spg, env. disease, antibiotics The salinity level in my moray tank has reached 1.030! I suspect that this is due to the addition of Epsom salts into my tank. <This is a lot of Epsom if so... it only needs to be added once... unless a good deal of water volume has been changed out> Should I change the water immediately? <Yes... I'd lower the spg to 1.025 in three days water changes... taking out a calculated volume of tank water and replacing it with freshwater.> Both my eels have not eaten for more than 1 month but that is a rather usual occurrence. My Soapfish is faring rather well in the tank at present. What should I do? <Start changing the water, NOW> The fishes seem normal presently but I do not want any nasty surprises. The tank currently also contains tetracycline (to aid the oxidized eel which is slowly recovering). If I were to change water, the tetracycline dosage would be diluted. Is this okay? <Yes, but I would NOT add more Tetracycline... not likely of value/use... your fish will heal with improvement in water quality, time> pH: 8.5 Nitrate & nitrite: 0.15 <Nitrite should be zero> KH: 8dKH Alkalinity: 3 meq/liter I figured out that the Epsom salts caused the rise in salinity. However, I need to still do a water change (last change was 3 weeks ago). However, I am afraid that if I were to top up both the Epsom salts and tetracycline, there would be tetracycline in the tank longer than the required dosage. This is because it takes time for tetracycline to be completely exhausted in supply in a tank. <Actually... the color of this antibiotic is persistent, but its activity only lasts a few days> I added tetracycline into the tank around 1 week ago. So, IMO, which may not be correct, if I add tetracycline in the top-up water, there will still be some tetracycline in the water about 1 week after the duration of the required dosage, which I fear may be bad for the fishes. <Me too... Do NOT re-add it> However, I also do not know the duration of the required dosage of tetracycline (not stated on package), and this makes things a tad more complicated. Difficult to explain. An example: Dosage for tetracycline: 5g (to be in water for 3 weeks). Tetracycline added. Further top up of new tetracycline 1 week later. 3 weeks later: Old tetracycline dosage exhausted (present in water for full 3 weeks), new dose only present in water for 2 weeks. Therefore some residual tetracycline stays in the water for 1 week more than required duration. Is that okay too? <Antibiotic use for marine fishes is tenuous at best... if administered NOT a good idea to place in their main tank itself... for loss of biological filtration, staining... reasons. I would hold off on adding ANY medication at this point. Lower your spg and supplement your biological filtration. Bob Fenner>

Refractometers hi guys:) <Hello...Jorie here> Quick question, I have 3 hydrometers and get a different reading off each and am fed up. I want a refractometer and don't mind paying the extra buck for quality.  I was wondering if you would feel comfortable with a refractometer from 1 one of the fallowing manufactures. Ocean Tech, Vital Sine,  Captive Purity. Which would you pick? Do you have a better choice perhaps? ocean tech, vital sine    http://www.drsfostersmith.com captive purity:   http://marinedepot.com    <I purchased the following refractometer about a year or so ago and absolutely love it.  Knock on wood, have had no problems whatsoever and would without hesitation recommend it to anyone in the aquarium hobby.  No need to pay the "big bucks" for all the bells and whistles unless you are a chemist, in my humble opinion! http://www.reefaquariumguide.com/sponsors/specials.php many thanks <You are most welcome.  Take care, Jorie>

More on Specific Gravity and Salinity (11/8/04) Steve, <Hi again> Thanks for the response. I have a couple more questions. As far as the Feather Dusters go,  I have had a couple of algae blooms since the tank is new, but nothing bad. <Good> How can I reduce the number of FDs I have now? <Cut back on excessive nutrients.> I have a couple of Wrasses in the tank, but they don't eat them. If I get something that will eat them, I also have a large FD and a Koko worm I don't want eaten. <There may be some smaller fishes that would only eat the smaller dusters, but they might start nipping the bigger ones when they run out of smaller ones to eat.> For the salinity issue with my tank, this is the description of my refractometer: Salinity Refractometer in a blue, foam-lined hard case. The RHS series of portable salinity refractometers are designed to measure the salinity of saline solutions similar to that of natural seawater. Improved viewing scales with larger, easier to read reference lines and digits. One scale checks the salinity levels with the range of 0-100 ppt (with 1 ppt scale divisions) <Yes, but this is not what is actually being measured here. Refractometers only measure specific gravity. The salinity scale they are using must be a correlation based on some reference temperature. Here is a good reference on this issue: http://www.algone.com/salinity.htm> and the other scale gauges Specific Gravity with a range of 1.000 to 1.070 (+/- 0.001 accuracy). Both enable the direct <No. The salinity is indirect.> determination of salinity in water that contains dissolved salt and little or no other dissolved solids. Hydrometers are nice, but they can be inaccurate. The RHS-10ATC is designed to be very accurate to protect your investments! All RHS models use ambient light, no battery or power source is required, making them truly portable. Models with the "ATC" suffix are equipped with "Automatic Temperature Compensation" for accurate measurements without recalibration after shifts in ambient working temperature (field use). <Ahh. So you are using some sort of fancy expensive model. Could be this temperature compensation mechanism does make the salinity measurement more accurate. How much did this cost you?> The right side of the refractometers view screen is the salinity measurement in PPT, and the left side is the SG. Just wanted to try to explain what I meant by using the salinity. <Understood. Nifty device. Still, I think you'd be find using SG and keeping in the range the LFS suggests. At a temp of 78F, a salinity of 35 correlates with SG 1.0245 at sea level, so 35 should be fine. I still am uncertain as to the effect of your altitude.> Thanks, Paul  <You're welcome. Steve Allen.>

Controlling salt levels I had many saltwater tanks for years and I never had mastered make up water and adding saltwater mixes.  How does one go about adding deionized water and salt mixed water adequately. << Not sure I understand. >> I can never seem to get the salt to mix all the way into the water before adding it to the tank. <Oh, okay.  I put four handfuls of salt into a 5 gal bucket.  Then I drop a powerhead in there and let it run for about 3 days.  Then I test the salt level.  It is always right on perfect for me. >> Also, I heard that the only water that needs to be added is RO or distilled water as make-up water but I don't think that that is true because a lot of salt ends up on the tank cover or around any of the tank openings. << You only need to add RO water.  The amount of "salt creep" that gets out is minimal.  Also, any time you add phytoplankton to your tank you are slowly adding a little more salt. >> Any suggestions?  Seems like every time I take something out or add fish, I have to test the specif. gravity of the water and re-mix some addition water. << This seems odd.  I've never worried about my salt level when adding a fish.  The fish is only going to displace a minute amount of water.  With a large rock or coral, I sometimes take out a couple cups of water from the tank, then put the new coral in. >> Pls. help.  I am just getting started in purchasing a reef system. << Best advise I can give is to just talk to some local friends when setting up your tank.  Ask them to watch and give advise.  For the most part salinity never changes, and I think most people go months without even testing it. >> Sincerely, Mpolka <<  Blundell  >>

Cheap Hydrometer Strikes Again (Or- Why You should Invest In a Refractometer!) Hi, Mr. Fenner!   <Actually, Scott F. in for Bob today> THANK YOU so much for maintaining these pages & CMA. <Will pass along the thanks to Bob!> I have had my 55 gal system for over a year, and something terrible happened this weekend.   <Uhh-Ohh...> First, let me describe the system: 55gal glass 70 lbs live rock 2" live sand bed no plenum no sump (yet) 260 W total VHO 6k + 10K + actinics CPR BakPak HOT skimmer 4 power heads = 200x tank volume/hour turnover Penguin mechanical filter w/ activated carbon filter pad Just got SpectraPure 25 gpd 3 stage R/O unit! ~12 big turbo snails ~35 hermit crabs 1 dragon wrasse (adolescent) 1 yellow tang 1 maroon clown 2 zebra Dartfish 1 coral beauty 1 blue-green Chromis Original water parameters: salinity 1.022 (**note this is what I THOUGHT it was!**), pH=8.2, temp ~78F, ammonia 0, nitrite 0, nitrate 30ppm (was starting to bring it down w/ new R/O unit when disaster happened), phosphate 2.0ppm. Here's what happened: unbeknownst to me, my stupid hydrometer that I was using to make all water change mixes over the last month was reading wrong!!!  It was reading artificially low, so I was (unknowingly) adding WAY too much salt to the mix.  This weekend, a horrible thing happened - the tank started to crash. <Ohh no!> I smelled the "rotten egg" stink of H2S, and all the snails died.  Algae out of control.  Even worse, the fish had white spots and were breathing hard - probably ich/crypt/Brooklynella contracted due to stress from bad water.  I quickly moved all 7 fishes into two quarantine tanks - a 10gal and a 20gal.  In the process of moving everyone into the QTs, I broke the hydrometer.  When I went out & got a couple more, I found out that it had been reading wrong!!!!  The salinity in the main tank & QT's was >1.04!  Horror!!!!  I wish I had known that a $3.00 hydrometer could cause so much damage.  ALWAYS make multiple independent measurements - I should have known that lesson from my job (I'm a space scientist).  Anyway, over the last 2 days, I've been bringing the salinity down to normal in all 3 tanks. <A lesson well learned- unfortunately, the hard way. I've experienced the frustration of inaccurate swing arm hydrometer before. My best advice is to purchase a refractometer. For as little as $50.00, you can purchase a high quality, precision instrument that will not let you down. Well worth the initial investment!> However, the poor fish still have ich or something like it - clown & tang are breathing fast.  All fish had spots.  I have treated both QTs with Mardel CopperSafe per the instructions.  Of course, the tough part is keeping the copper concentration right while doing the 50% water changes each day that are necessary to control ammonia. <Yep...a balancing act> I also dosed the 10 gal (which contains the tang, clown, & Chromis) with malachite green on the off chance that Brooklynella is also present (which is not cured by copper).  I have raised the temps in both QT's to 80F to try to speed up the lifecycle of the disease.  I am letting the main tank run fallow (although I left the hermit crabs in it - they seem bulletproof), especially since a lot of stuff on the live rock died, with as high a temp as I can get from the heaters, 85F.   <I see nothing wrong thus far...) This would all be fine and good, as I know that I can maintain the system stably like this for the 4-6 weeks necessary to reduce the parasite load and "recure" the live rock.  Here is my problem: on Oct 27, I have to go out of town for work for 10 days.  I don't have a reliable fish sitter lined up yet.  Any ideas here of what to do?  I was thinking that after 2 weeks of copper treatment, the fish can come out of their small QTs and could possibly go into a big (like 50 gal or greater) plastic bin that I could set up.  Then a fish sitter could come and change say 20% of the water every day to control ammonia.  No gravel or anything else in it, just the sponge filters and a couple of power heads.  What do you think? <A very good idea. I would not continue use of copper sulphate (or any medication) while the fishes are in the care of an inexperienced guardian. You might also want to utilize some Poly Filter pads (perhaps in an outside power filter, or even just "passively" in the container) to help remove some ammonia.> Would they be okay like this, assuming I could get someone to do the water changes?  Is there any way to speed up the cycling of my main tank so I could put the fish back in before I leave? <Should be fine. I'm not really aware of any way to "speed up" the process. Basically, running a tank fallow is an attempt to interrupt the life cycle of the causative protozoan. Let the passage of (the correct amount of) time be your ally.> Should I add live rock to my QTs after I'm done with the copper to put a biological filter in place to help keep ammonia down while I'm gone?  Massively confusing. <It is a bit confusing. Keep in mind that there is no one "right" way to do everything. All any of us here at WWM can do is speak from our experience. It certainly would not be harmful to add some cured live rock, although the biofiltration benefit may be quite limited.> Thank you SO much for your help!  I am very attached to these fish, and I truly want them to have a nice life.  I don't want them to have to suffer for my ignorance.  I feel terrible that this happened. Amy <No need to be hard on yourself, Aay. These kinds of things happen to hobbyists at every level (even to space scientists!). Part of the (unfortunate) learning curve of the hobby. With dedication and patience (which you have large amounts of!), you'll be able to overcome this calamity and continue on the path to long term success! Good luck! Regards, Scott F.>

Specific Gravity for a FO Marine Aquarium (8/13/04) What is the lowest advisable permanent specific gravity for a FOWLR tank containing Lionfish and a Porc. Puffer? <1.017 to 1.020> I have heard the lower the S.G., the lower the chances for parasitic infestation (within reason of course) is 1.021-1.022 too low? <Nope should be fine and you can go even lower in a FO marine set up to between 1.017 and 1.020, with the exception of fish from the Red Sea where natural specific gravity is higher @ 1.027, Achilles tangs, some seahorses, and several fish that have symbiotic relationships with invertebrates like clownfish. These require a consistent specific gravity of 1.023-1.025 to thrive. For additional information on specific gravity in marine systems please have a look at this article.........http://www.wetwebmedia.com/spg_salinity.htm

Permanent Hyposalinity For A Marine Tank? 7/29/04 I was wondering if it would be okay to house marine fish without any inverts in 1.008 to 1.012 salinity for good?  I've heard that low salinity is very easy on these fish and reduces stress significantly and kills off marine diseases used to 1.026 salinity (normal sea water). <Well, there are a lot of opinions out there on this subject. Many wholesalers and transhippers may keep fishes in lower specific gravities in order to help lower the possibility of parasitic diseases. However, in the long term, such low specific gravities may not be safe. I've read of studies that have demonstrated that fishes have suffered damage to their internal organs as a result of long-term exposure to an unnaturally low specific gravity. If it were me, I'd stick to 1.022-1.025 (I like 1.025) and be done with it! Fishes have evolved to live in these specific gravities over the eons, and it works just fine. Why change things now! Regards, Scott F>

Salinity levels Hello Boys, <Hi Chris; you managed to get one of the girls here, MacL.> Got a easy Q&A for anyone so you don't have to run away. I have a 500lt marine tank the salinity is 1.027 due to topping off with salt water. I need to get it back down to 1.025 how much plain water do I need to use to get this back to normal. <I prefer to take this down very slowly so as not to stress the fish. I would do 25% water changes with a salinity of 1.018 every couple of weeks until you get it down to the appropriate levels. You can just add top off water and take it down a bit but you'd want to be very careful about not doing this too drastically. Good luck, MacL> Ta Chris P.S. is Anthony on holiday or is he not answering my e-mails.. <Right now Anthony is on a speaking engagement, I am sure nothing personal is meant by it whatsoever.>

Measuring Salinity (7/20/04) Hello Crew! <Steve Allen tonight> It's been a long time since my last question, which I hope you will translate into a fair amount of success on my part due to the sage advice and guidance given here. After 1 1/2 years of operating my mostly fish only tank, I have discovered that my trusty ol' SeaTest Specific Gravity Meter (which was at least 8 years old, due to other attempts at this hobby) was giving me flawed readings.. I discovered this, because I decided to purchase a new meter just a double check to the old.. sure enough.. they varied.. <Ando how do you know that the new one is right?> According to the new meter I was running at 1.028, so I've began lowering to 1.022 (only .001 drop per day). Now that I'm at 1.022 I've noticed my live rock is releasing tiny air bubbles over the past 2 days. What is the tank trying to tell me? <Perhaps that you need a more accurate way to measure salinity--a hydrometer. I'd take a sample to a store that uses one and have them verify your reading. Hope this helps.> Thank you again for your service, I've enjoyed it and have passed on this web address to everyone who is not aware of you. Your friend, Daver

Specific Gravity and Salinity Question Hi, I have a 75 gallon F/O NLR community saltwater tank with 2 false perculas, 1 flame hawk, 1 coral beauty angel, 1 butterfly and 1 royal Gramma.  Please tell me the lowest susceptible and healthy specific gravity I can keep the tank at.  thanks, James <James, Ryan with you today.  The lowest specific gravity I would use on a permanent basis is 1.017-1.020.  The slower you can bring your water to these levels, the less stressed your livestock.  Good luck, Ryan>

HYDROMETER QUESTION Hi, <Hi James> I would like your opinion of a hydrometer.  I saw a Tropic Marin in Foster's and Smith catalog for $16.  In your opinion, is this a reliable instrument?  <That type of hydrometer can be pretty reliable, they are however limited to what they are, and that's not totally going to give you an exact specific gravity in your tank in my opinion. I'd like to refer you to the thread on specific gravity and salinity on the website James take a look at this I think it will help you make your decision. http://www.wetwebmedia.com/spg_salinity.htm> thank you, James <Good luck, MacL> James Hall

- The Gravity of Specific Gravity - My saltwater tank is all setup but the specific gravity of the water is 1.017. I was wondering if this is still safe for marine fish. <Not for extended periods. It's in your and your fish's best interest to keep the salinity in the 1.020 to 1.025 range.> Thanks <Cheers, J -- >

Salinity Out of Whack (4/22/04) I am having a terrible time with getting my salinity to remain constant. After reading some articles, part of my problem could be my plastic hydrometer. But it seems no matter how much salt I've added, after awhile it drops down to 1.020, the lowest "safe" zone. <Where does it start?> I'm afraid the live rock that is in there will be affected. Any suggestions? I'm frustrated beyond belief. Thanks so much, Jen <Well Jen, this seems like a really frustrating problem indeed. The first thing I'd do in your shoes is invest in a decent refractometer. The good ones cost $80 to 100 dollars on line. I consider mine to be money well-spent. Check www.marinedepot.com or www.drsfostersmith.com . This way you can trust your readings. What brand of salt do you use? Some are more reliable than others. Salt shouldn't just disappear. In fact, your SG should creep up a bit as water evaporates. How often do you do water changes? What SG is your change water. Sorry to pepper you with questions, but this is a strange one. Get some refractometer numbers and see what you get. Send along some more info and we can hopefully figure this on out. Steve Allen.>

More on Out-of-Whack Salinity (4/22/04) Thanks for your reply. <My pleasure.> I seem to get different readings all the time. <A more accurate and reliable instrument is a must here.> Even testing multiple times, I will get different readings. This tank is new, it's a Nano Cube (12 gallons). <Small tanks are harder to keep stable, but SG should not drop like you are reading.> I've had it running for months now and only have live rock and live sand in it. No fish. <Good, wait until things are stable.> I will look into the refractometer - thanks for the suggestions. <You will not regret the purchase.> As far as brand of salt, I used the Instant Ocean by Aquarium Systems I believe. <A reliable brand.> I've done a few water changes. And that seems to be very difficult to match the exact numbers to the tank numbers. What's the most effective way to do that? <I'm not quite sure what you mean here. Mixed as per the directions, IO will reliably come to the SG specified on the label. Evaporation is replaced with fresh (no salt) water.> How often do I need to do that with nothing in the tank? <Not very often, maybe once a month.> I've been trying to learn as I go, so I appreciate any help you can give me. <Do you have any books? I highly recommend Michael Paletta's "The New Marine Aquarium" and Bob Fenner's "The Conscientious Marine Aquarist." Thank you very much! Jen <You're welcome. Keep us posted. Steve Allen.>

- Testing the Waters - Hello! I've been reading through the thousands of chat information you have about tank setup and had a few questions. I recently purchased a Glass Tropic Marin Hydrometer and a Instant Ocean Plastic Hydrometer for backup or comparison. After reading more on various web sites I was told that I would need a Refractometer and that the glass and plastic models are inaccurate and vary too much. Is this true? <Not entirely... the Tropic Marine hydrometer you have is a quality instrument and should be reasonably accurate. Most all swing-arm hydrometers are usually accurate, but not well calibrated - that is to say, they will read consistently but they may be off by 0.001 or more.> And if so can the cheaper Portable Refractometers($50.00) be used or is the more expensive full Ocean Tech($100.00) required? <Refractometers all operate the same way... just the build quality of the instrument will suffer.> Just see so many people going back and forth on this that I wasn't sure and figured the master reef keeper would know. <I use my refractometer to calibrate my swing-arm hydrometer.> Also I am debating over the test kit to use and which tests. I've been told to stay away from the Aquarium Systems kits and go with the Salifert ones. The Salifert tests are more but are they that much better or worth the money? <Yes, although the Aquarium Systems tests are decent - I'd avoid the Aquarium Pharmaceuticals and Red Sea tests.> Or do you know of another test kit? <LaMotte or Hach... but these will cost you even more.> I heard SeaChem also to be good but less then Salifert. I don't mind spending the money for a good product. As for which tests, I was thinking: phosphate, nitrate, calcium, ammonia, nitrite, nitrate, pH, Alkalinity <At the very least nitrate, pH, calcium, and alkalinity.> I told that after I cycle the tank with my live rock that I wouldn't need the Ammonia or Nitrite tests. Does this sound correct? And do I need a low range nitrate after cycle? <Yes and yes... if you are in the money spending mode, then having all those tests won't hurt you, but it's true that you won't use ammonia or nitrite very often after your tank is cycled.> And finally I was going to use ESV KALKWASSER to replace the calcium and baking soda for a buffer. Do you recommend any other supplements or items I need to add to treat the water? <Sounds good to me.> Thank You for your great advice and web site, J <Cheers, J -- >

Optimum Salinity? (4/7/04)   Hello, <Steve Allen with you today>   I am just wondering, in particular what the recommended salinity levels are. My 3ft Salt Water Aquarium is currently at 34ppt. It has been running about 6 weeks and so far I have only introduced 2 Chromis as I plan to take things slow. They seem to be very healthy and look great. Is that a good place to be? I hear optimum is between 34-36ppt but also hear other figures. <I prefer to imitate the natural seawater these creatures have lived in for millions of years, so 34-36 range is appropriate. Some recommend lower levels for to principal reasons: 1-it may reduce parasite infestations, but proper quarantine is far more effective. The levels you have to go down to are unhealthy for inverts. 2-to save money on salt, which I personally do not consider a legitimate reason for subjecting these creatures to an unnaturally low salinity. Most people measure "salinity" as specific gravity, which is not the same. At common tank temps, the numbers you cite correlate with 1.025-1.026. I keep my tanks at 1.024-1.025. Read more here:  http://www.wetwebmedia.com/spg_salinity.htm and here: http://www.ntlabs.co.uk/specific_gravity.htm Any advice on what the recommended reading should be would be appreciated. <"The Conscientious Marine Aquarist" by our very own Bob Fenner and "The New Marine Aquarium" by Michael Paletta.>

Salinity  Dear Bob,  <James>  I've just read the chapter on salinity and am still not to sure what to shoot for. In my 70 gallon tank I have a Purple Tang from the red sea and live rock which both like high salinity 1.025-1.027. I also have a Regal Tang, Yellow Tang, Niger Trigger and a Clown fish which all do better in salinity of 1.017-1.020. What do you think?   <I would settle on near seawater spg of 1.025>  Also I want to buy your book The Conscientious Marine Aquarist. I have found one published in 1998 (Amazon, can't find it here in Cape Town).  People on the site keep saying they are looking forward to your new book.  Is it the same one or is there a new one on the way?  <Ahh! A series of works "The Natural Marine Aquarium", the second volume is in process... on reef fishes. The Conscientious Marine Aquarist is a general marine aquarium work, and the NMA series more in-depth coverage on reef livestock and husbandry topics>  Many Thanks, James Barclay  <Thank you for your query. Bob Fenner>

HELP!  My SG is way too high! Hello and thank you ahead of time for helping me out. <Glad to help> Ok, here is what is going on.  The last week or so I have noticed that my polyp corals have not been looking too good.  They were fine the last 2 months or so and now they are looking sort of shriveled up.  All my fish and other inverts (shrimp, snails, hermits, serpent star) are doing fine. This morning I tested every parameter that I could and here was the results:  Ammonia 0, nitrites 0, nitrates 10, pH 8.3, dKH 9, calcium 475, iodine 0.06, phosphates 0, and SG 1.025.  55 gal minireef with 60#LR. I called my LFS and they said it sounded like SG problems.  I brought in my hydrometer and water sample to compare readings with their refractometer to see if it matched.  Well, my hydrometer is way off and my water is at a SG of 1.0295!!!!  I purchased a new one (and calibrated it there in the store and it is dead on).   <Yeeikes!> Here is my plan of action, tell me if it is ok or what I need to do differently if I am wrong.  I am going to remove 1 gal of tank water and replace with fresh RO/DI water (no salt added) every day until SG comes down.  I will closely monitor all other parameters and tank inhabitants for any changes. Sound right or do you have an alternate solution?   <Does sound like the best possible plan> Sorry to bug you but I could not find someone with my specific problem in the FAQ's.  This one is frustrating because it was due to faulty testing equipment that I purchased 3 months ago, and I really don't have the money to keep replacing stuff.  I really can't afford a refractometer either so the plastic ones will have to do. <As long as you can rely on yours to be precise (to give you the same measurement consistently... even if it's not accurate. Bob Fenner>

Salinity / Specific Gravity Calculation OK, first off, yes I am an engineer. <Okay> Now that I have that out of the way, here's the lowdown.  I am new to the marine aquarium hobby (as of a week ago I would have called this the saltwater fish hobby and probably been shot for it) and am in the process of setting up my first tank.  I am trying to get the salinity of the tank correct before I add any fish to it, but can't seem to get it set correctly. I now know that I need approximately 130 g of salt per gallon of water for a NEW setup (I'm using Instant Ocean brand of salt), but what I want and can't seem to find anywhere is a method for calculating the amount of salt required to raise the specific gravity of a gallon of water 0.001. <Would be a proportionality of the parts per thousand... 1/35 or 0.001/0.035 equals X/130 grams of salt mix...> For example, I know that I have a 50 gal tank at 76 degrees F and a specific gravity of 1.015.  I would like to raise the specific gravity of the tank to 1.020.  How much salt will I need to add to do so? <Mmm, five times the above proportion, let's see: 5 X 3.714 or 18.57 grams... per gallon, actual gallons...> I'm CERTAIN that there is an easy mathematical calculation for this.  I probably even learned in it college at one point in time, but have since forgotten it.  Unfortunately, I've already performed one 50% water change to lower the salinity below the too high to be measured range, and want to avoid having to do another.  Since that time, I've added very small amounts (approximately 1/8 cup) of salt a couple of times and not been able to register any measurable difference on my (crappy) plastic box hydrometer (from reading the various FAQs on your site, it appears that I will need to invest in a refractometer, if not a digital hydrometer, and that my box hydrometer will measure about 0.002 low on the SG scale due to the difference in temperature of the tank to the calibration temperature).   <A refractometer may be a worthwhile investment... but please see below> Is the unperceivable change due to the hydrometer that I am using, or am I simply not adding enough salt to make a difference? <Likely mostly the former> Anyway, thank you in advance for your help.  I'm currently in the process of reading your book, and I can see already that it is going to be a big help (my future fish thank you too!) <You are all welcome. I encourage you to read over this area on our site re mixing, storing synthetic seawater: http://www.wetwebmedia.com/water4maruse.htm The gist of it/this is I would pre-mix and store your water... get it about where you want it spg wise... and nudge where you are now... and adjust at whatever interval for evaporation, splash... and not get too involved in rusting out your gram scale balance. Bob Fenner> Sincerely, Jason Oldfield
Re: Salinity / Specific Gravity Calculation
Bob (and crew), <Jason> Thank you SO much for your response.  Though I don't anticipate having to measure salt down to the gram, your insight has given me at least a place to start with regards to adjusting the salinity in my tank, which is 1 cup of salt equals an increase in specific gravity of approximately 0.001.  I tested this last night and it works, so I'm thrilled (it's sometimes hard for us newbies to know what to do!) <Mmm, okay... but still encourage you to pre-mix, store your synthetic for the reasons archived> I do have a question for you though regarding advance water preparation. How long in advance can you make your water before you use it?   <Indefinite period... it doesn't "go bad"> I've read (I believe in your book) that you should make it and store it at proper temperature with adequate circulation for at least a week before using it. <A week is about ideal> I only have a 29 gallon tank, so I'm thinking that I will probably make water in large enough batches that it will probably last me a month (or maybe more).  Is this OK? <Sure> Also, for a tank of this size, would you still recommend small weekly water changes of about 2 gallons, or is that too frequent? <See WWM re more frequent, even smaller percentage changes... ScottF has a very nice article on this practice> My local dealer said that monthly water changes were probably all that was necessary, but I'm thinking that more frequent water changes can't hurt, AND if I do it weekly I can make it part of my regular Saturday morning routine (rather than trying to remember the last time I performed a water change, which would most certainly lead to it not getting done on a regular basis.) <Bingo... I am of the same mind/mentality as you> Anyway, thank you again for your response.  I am currently in the process of cycling my tank with live rock for the next few weeks before I add any fish, which should give me a chance to catch up on my reading.  But, I'd be shocked if I didn't have any more questions for you, so be prepared! <Will try to be> Looking forward to getting my first fish and critters, Jason Oldfield <Outstanding. Bob Fenner>

When should I stop? Quick Question. At what point will lowering the specific gravity adversely affect my biological filter media?  At what point will it stop to grow good bacteria on the media.  Specific #'s would be great. <NSW, near sea water conditions are best. That is, a specific gravity of 1.025 is ideal... and keeping this about here (topping off regularly, adjusting new water carefully) is very beneficial. For treatment with hyposalinity, any drop/change in spg will adversely affect nitrification. ANY. You should monitor aspects (ammonia, nitrite) daily, be ready with new water for dilution, perhaps chemical filtrants, pre-made biological filter material... if lowering spg, or raising it.>          If you want some details leading up to this question read on, if not thanks for your help!         I have a 120 gallon main tank a 20 gallon quarantine and a ten gallon hospital.  All tanks are biologically alive with all parameters in check.     The reason I have all the tanks going is that I just got a majestic angel about a week ago, I know what you are thinking but I did my research and realize what I'm up against and took 7 months of going to my LFS to find the perfect specimen.  The problem occurred when I introduced some Caulerpa to the main tank for a treat for my powder blue after a quick rinse without quarantine," bad move". I've been doing this for 5 years now, will I ever learn.  Within about 5 days the tang had some spots, I caught him gave him a dip then returned him home. Three days later you know what.  Unfortunately I'm in it for the long haul now at least 45 days.              So now I have three tanks set up and running. A ten gal hospital bare bones with a powder blue in it which I'm am treating with hypo salinity and formalin dips plus my own tank/filter creation which has a high enough turn over rate to successfully filter out that pesky littlie protozoa but allows me to segregate the bio filter. A 20 gallon quarantine tank with 8lbs of live rock, live sand, tang haven algae two power heads and a whisper 30-60 which I modified and put  bio wheels in to boost it's efficiency, one Chromis and a majestic angel.  Did I mention I have now found a few spots on the angel?   <Now you have> So let's break it down I have three tanks with ick and five fish I have to find a place for to let the main tank go fallow for about two months.  Yes. I do have cleaner shrimp but about all they're good for is making babies and stealing food from the Anemone, Its a good thing my two Perculas are great protectors.  I have a written protocol for all new fish but slipped on the algae.  I always use my quarantine first then if the new fish have parasites I put them in my hospital which I will establish 1 week or more ahead of getting a new fish by a sponge filter from my main tank  then I can let the quarantine go fallow for a month while I treat the new fish in the hospital tank without drugging up the water then after one month they go back in the quarantine tank for another two weeks. I always try to keep from using meds, except in dips, if I can at all avoid it.  If there still alive after all this then they make it into aquarium paradise, if not then at least I didn't contaminate my main display. I have about a 85% success rate.  I thought I had a fool proof system. I guess the fool didn't fallow the system.                    Without the books of Bob F. and articles on this site I wouldn't have ever stayed in this hobby.  You guy's are the Bomb! <Be chatting, Bob Fenner>

Become a Sponsor Features:
Daily FAQs FW Daily FAQs SW Pix of the Day FW Pix of the Day New On WWM
Helpful Links Hobbyist Forum Calendars Admin Index Cover Images
Featured Sponsors: